Method of processing mixtures of carboxylic acids



molecular weight acids.

United States Patent lice METHOD OF PROCESSING MIXTURES OF CARBOXYLIC ACIDS Otto Grosskinsky, Bernhard Jiittner, Walter Klempt, and Walter Thiirauf, Dortmund-Eving, Germany No Drawing. Application August 9, 1955 Serial No. 527,406

Claims priority, application Germany August 12, 1954 7 Claims. (Cl. 260-475) The present invention relates to a method of separating low molecular weight carboxylic acids from a mixture containing the same and further containing high molecular weight carboxylic acids, and particularly to a method of separating mixtures of dark colored high molecular weight carboxylic acids and light colored low molecular weight carboxylic acids produced by the nitric acid oxidation of carboniferous material.

Upon subjecting fossil from more recent solid combustibles to an oxidizing treatment carried out in an acid medium, preferably by means of nitric acid on such carbonaceous material as bituminous coal, lignites, peat, coke, tar and pitch, dark colored crude mixtures of carboxylic acids are obtained, these mixtures substantially consisting of higher molecular weight carboxylic acids and lower molecular weight carboxylic acids such as benzene carboxylic acids and aliphatic carboxylic acids in a manner such that the light colored low molecular weight acids are separated in the form of their esters,

Other objects of the present invention and advantages thereof will be apparent from a further reading of the specification and of the appended claims.

With the above and other objects in view, the present invention mainly consists in a method of obtaining low molecular weight carboxylic acids from a mixture containing light colored low molecular weight carboxylic acids and dark colored high molecular weight carboxylic acids, comprising the steps of subjecting the mixture to a thermal treatment at an elevated temperature until the dark colored high molecular weight carboxylic acids are converted to a product insoluble in a solvent in which the light colored low molecular weight carboxylic acids are soluble, thereby forming a reaction mass including {insoluble constituents and soluble light colored low molecular weight carboxylic acids, dissolving the light colored low molecular weight carboxylic acids in a solvent therefor, said insoluble constituents not being dissolved, and recovering the light colored low molecular weight carboxylic acids.

The nitric acid oxidation of carboniferous material such as bituminous coal, lignites, peat, coke, tar and pitch results in the formation of a reaction mass con taining valuable and less valuable products. The less valuable products'are mainly in the form of dark colored (e. g. mellithic acid, benzene pentacarboxylic acid, pyromellithic acid, mellaphanic acid, trimellithic acid, phthallic acid, adipinic acid, succinic acid, and oxalic acid). It is extremely important to provide a method of separating the single constituents and, if possible, separating at least distinct groups of substances. The *most important group of substances which must be separated from each other are the higher molecular weight dark colored carboxylic acids from the light colored lower molecular weight carboxylic acids, since the latter are starting materials for the production of many important industrial products such as excellent plasticizers, resins and lacquers.

Various processing methods have already been proposed, these methods aiming mainly at separating in a satisfactory manner the light colored lower molecular weight carboxylic acids from the dark colored higher The higher molecular weight acids can be precipitated and readily removed for example by digesting the crude mixture of carboxylic acids I in water and adding inorganic salts if required. Furthermore, the low molecular weight acids can be recovered by selectively extracting the crude mixture of carboxylic acids.

,light colored low molecular weight carboxylic acids from a mixture of the same with dark colored high' molecular weight carboxylic acids.

It is another object of the present invention to provide a method of separating light colored low molecular weight polycarboxylic acids from a mixture of the same with dark colored high molecular weight polycarboxylic acids high molecular weight carboxylic acids, while the valu-' able and economically desirable products are in the form of light colored low molecular weight carboxylic acids such as benzene carboxylic acids and the aliphatic polycarboxylic acids eg mellithic acid, benzene pentacarboxylic acid, pyromellithic acid, mellophanic acid, trimellithic acid, phthalic acids, adipinic acid, succinic acid and oxalic acid. For the purpose of convenience, throughout the specification and claims in this case, the valuable products such as the above named will be referred to as light colored low molecular weight carboxylic acids, while the less valuable organic products produced by the nitric acid oxidation of carboniferous materials will be referred to as dark colored high molecular weight carboxylic acids. Even without the above explanation, this designation of dark colored high molecular weight carboxylic acids and light colored low molecular weight carboxylic acids clearly defines the separate group of substances to those skilled in the art.

We have found that by subjecting a mixture of dark colored high molecular weight carboxylic acids and light colored low molecular weight carboxylic acids, particularly such mixture'as is produced by the nitric acid oxidation of carboniferous material, to a thermal treatment, the undesirable dark colored higher molecular weight acids are rendered insoluble by the treatment while the desirable light colored low molecular weight carboxylic acids are substantially unaffected. The crude mixture of the two types of acids may be subjected to the thermal treatment either in the form of the dry mixture or dissolved in water or an organic solvent liquid or mixture of organic solvent liquids. By thermal treatment we of course mean the heating of the mixture to a temperature sufliciently high to affect the higher molecular weight dark colored acids without substantially atfecting the lower molecular weight light colored acids. The time of the heating will of course vary depending upon the particular temperature used, but is generally in the neighborhood of several hours. The thermal treatment according to the present invention very simply results in a. method of separating the valuable light colored lower molecular weight acids from the relatively not valuable dark colored acids by rendering the latter insoluble in most solvents while the former still remain in their original state and therefore soluble in all solvents.

Patented Mar. 24, 1959 in which they are usually soluble, e.g in water and organic solvents. M The thermal treatment according to the present invention is preferably carried out at a temperature above 100' C. and most preferably at a temperature between 1.00 and 250 C. The method, of the present invention can therefore be carried out by subjecting the dry crude mixture of dark colored high molecular weight acids and light colored low molecular weight acids to such thermal treatment whereupon the thermally treated product is digested with a solvent which ordinarily would dissolve the entire crude product if the same had not been subjected to the thermal treatment. As a result of the thermal treatment, a considerable portion of the solid matter remains undissolved, this portion substantially consisting of the dark colored high molecular weight carboxylic. acids (converted to other substances by the thermal treatment) which'have a low market value. The important light colored acids are dissolved by the solvent and can then be recovered by any suitable manner, for example by filtering off the undissolved constituents, separating the solution from the filtered undissolved constituents, evaporating the solvent of the solution and thereby recovering the light colored low molecular weight carboxylic acids. The thermal treatment results in a decarboxylation or decomposition of a part of the solid substance of the crude mixture, as explained above, this part being the dark colored high molecular weight acids, resulting in the evolution of carbon dioxide, nitric oxide, water vapor and other gases. Preferably during this thermal treatment steam or some other gaseous medium is used to remove the evolved gases. The thermal treatment according to the present invention. may be carried out on the mixture of dry acids as indicated above, or also in the presence of a liquid medium, the mixture of carboxylic acids either being completelyor only partially dissolved in the liquid medium. Thus, suspensions as well as solutions or partially dissolved mixtures of the high and the low molecular weight carboxylic acids may be subjected'to the thermal treatment according to the present invention. The consistency or concentration of the materials to be treated may be arbitrarily chosen. If it is desired to subject the crude mixture of high and low molecular weight carboxylic acids to the treatment according to the present invention in dissolved condition, water, alcohols, ketones, esters, ethers or as a matter of fact any solvent liquid or mixture of liquids capable of dissolving the crude oxidation prodnets are suitable. According to a preferred embodiment of the present invention, when it is desired to produce the esters of the low molecular weight carboxylic acids, the particular alcohol with which the acids are to be esterified may be utilized as the solvent liquid or as a portion of the solvent liquid. According to the preferred embodiment of the present invention, the crude starting product resulting from the nitric acid oxidation of carboniferous material, after the removal of the excess non-reacting nitric acid, is dissolved in water to form an aqueous solution thereof, which aqueous solution is directly treated and subjected to the thermal treatment whereby the dark colored higher molecular weight carboxylic acids are rendered insoluble and easily separated from the remaining aqueous solution of the light colored lower molecular.

weight carboxylic acids.

On the other hand, as indicated above, this thermal treatment can be applied also to an extract obtained by digesting crude mixtures of carboxylic acid with an or- .ganic, solvent liquid which may either be non-reactive or may be reactive as in the case of alcohols. When heating .an alcoholic extract, e.g., a methanol extract, to atemperature of about 180 C. on the one hand higher mole'eular weight carboxylic acids are precipitated and on the other handjthe lower molecular weight acids are esterified. Thus, the thermal treatment conditions ofthe "carcas present invention may be chosen so as to not only convert the dark colored higher molecular weight acids into in"- soluble compounds, but also to effectuate a complete esterification of the light colored lower molecular weight acids. The most favorable conditions of processing vary depending upon the alcohol utilized and simple pretesting can determine the most suitable conditions for any particular alcohol with any particular crude starting material. If the esterification is incomplete, a second esterification can be provided, preferably after first having removed the insoluble matter from the solution. Finally, esters so obtained can be converted into mixtures of the desired acids, for example by hydrolysis with water under super-atmospheric pressure. p

In general, the mixtures of soluble acids obtained after separating the insoluble constituents resulting from the thermal treatment of the higher molecular weight acids, are not quite colorless, the color depending on the oxidizing treatment employed and the manner and time of the thermal treatment. A bleaching may be achieved by a subsequent treatment with decolorizing adsorbing agents, such as bone black or bleaching earth, or by treatment with the usual oxidizing agents such as nitric acid, chlorine, chlorine dioxides, hydrogen peroxide, potassium per manganates, chromates, etc. Since the process of the present invention per se results in a comparatively pure product, only small amounts of the above mentioned oxidizing agents are required. When using chlorine, a chlorination takes place together with the bleaching, most valuable chlorinated products thus being obtained. Such additional treatments when applied to esters result in decolorizing the same, and when utilizing chlorine, in a simultaneous chlorination, thus yielding products which are excellent plasticizers.

In addition, the method of the present invention described above can also be applied as a finishing method to the separated low molecular weight acids which, in most cases, are still somewhat dark colored. These acids can be dissolved, for example in water, simultaneously lowering the acidity by adding alkaline substances or by the addition of salts, such as sodium chloride or sodium sulphate, whereby additional small amounts of dark colored acids are salted out. The addition of the above mentioned chemicals can be carried out also before separating the acids rendered insoluble by the thermal treatment of the present invention. Consequently, the ingredients rendered separable by the latter treatment according to the present invention can be removed separately or together with the ingredients rendered in soluble by the thermal treatment. When processing a product obtained by oxidizing a combustible rich in ashes, the amount of substances rendered separable by thermal. treatment is much larger, the mixture of low molecular weight carboxylic acids already being obtained very pure. The low molecular weight acids can be recovered in very pure condition from their aqueous solutions obtained according to the present invention by extraction with selective organic solvent liquids. Finally, it is possible also to subject the low molecular weight acids to sublimation, this method yielding the purest product.

The higher molecular weight acids separated by the method of the present invention can be used as base 'mineralsalts of metals from the first, second and/or eighth groupof the periodic system.v For example, salts 'ofsuch metals as copper, silver, zinc, cadmium, mercury,

ally of minor commercial importance.

pare these esters, it might be possible, of course, to sub- .ject the crude oxidation product to a thermal treatment iron, cobalt and nickle may be utilized. Salts of these metals when added to the crude oxidation product apparently have the effect of promoting the decarboxylation of the dark colored high molecular weight-carboxylic acids to form additional amounts of light colored low molecular weight carboxylic acids, whereby the yield of the latter is perceptibly increased. It is certainly possible that in addition to the decarboxylation, various other eifects are involved by adding such salts, e.g. catalytic decompositions, all of these in fact contributing to decoloring the oxidation product and increasing the yield of light colored carboxylic acids.

. In commerce, the light colored low molecular weight carboxylic acids of the above mentioned types, particularly the benzene carboxylic acids or mixtures thereof, are demanded preferably in the form of esters, whereas the free carboxylic acids or mixtures thereof are gener- In order to prein the presence of water, as pointed out above, then to 1 separate the insoluble dark colored substances, and finally to esterify the light colored carboxylic acids obtained in the form of an aqueous solution thereof. By proceed- .insoluble product. However, in accordance with the pres- .ent invention, it has been found that this is not necessary in order to produce substantially pure products, e.g.

it is not necessary to eliminate the dark colored substances prior to the esterification of the light colored low molecular weight carboxylic acids since the dark colored substances essentially do not react with alcohols to form esters, despite the acidic nature of the dark colored substances. This practically passive behavior of the dark colored substances offers the possibility of doing away with the separation of these substances so that it is possible to subject the entire mass of both dark colored and light colored substances to a simultaneous thermal treatment and esterification which may be carried out in the same vessel and without any intermediate treatment, doing away in this manner with the necessity of removing the bulk of water by distillation.

Moreover, we have found that the above mentioned thermal treatment of the crude oxidation product and the esterification of the light colored carboxylic acids can be combined with each other in temporal and spatial respect so that both steps are integrated to form a single step. In such combined process, the light colored low molecular weight carboxylic acids are substantially esterified, as pointed out above, while the dark colored high molecular weight compounds remain undissolved andcan' be separated from the dissolved low molecular weight acid esters by filtration.

Nevertheless, the obtained filtrate may be more or less colored due to the presence of small amounts of dis solved dark colored products. Such mixture of esters cannot be directly worked up by distillation but require an intermediate additional purification by extraction with a suitable organic solvent liquid, this step being somewhat undesirable and therefore a complication of the entire process. However, it has been found in addition that surprisingly pure solutions of esters can be obtained by carrying out the thermal treatment of the crude oxidation product under superatmospheric pressure and in the presence of an alcohol or alcohols, and, in addition, in the presence of a non-polar organic solvent liquid, or mixture of non-polar organic solvent liquids, such as for example gasoline, petrol spirit, ligroin, and the like. In such case, the higher molecular dark colored carboxylic acids are so completely precipitated that the dissolved esters after having been separated can be directly processed by distillation. Accordingly, the process is based on the fact that when esterifying under superatmospheric pressure and in the presence of'a non-polar solvent liquid, the entire amount of dark colored high molecular weight compounds contained in the oxidation product is com pletely precipitated, and decarboxylation of higher molecular oxidation products taking place simultaneously, as is apparent from the fact that carbon dioxide is evolved in considerable amounts. The higher molecular constituents are precipitated as a peculiar granular mass which can be easily removed. In this process not only is an extraction superfluous, but the lower molecular masses are completely esterified and the higher molecular compounds are separated in a single f operation. The crude ester mixture obtained need only be separated from the organic solvent liquid and subsequently purified by distillation in vacuo.

'Ihe distillation of the mixture of esters is preferably carried out according to the well known falling film method. After having distilled off the excess alcohol or alcohols, the remaining esters of the low molecular weight carboxylic acids are comparatively viscous so that, owing to the high viscosity of the same, it is not possible. to distill the esters according to the usual methods, evenunder high vacuum, therefore, a falling film vacuum distillation is utilized which allows for completedistilla' tion of the entire esterified product, a small greasy residue and a very good yield of ester distillate thus being obtained.

The precipitation of the high molecular carboxylic acids proceeds more rapidly than the esterification under superatmospheric pressure, even when accelerating the esterification by continuously distilling off the water formed. The alcohols and the non-polar solvent liquid are distilled ofi together with the water. If necessary, the organic liquids are continuously supplied by automatic reflex after having separated the water in atrap. Since water present from the start does not substantially affect either the esterification or disturb in any way the precipitation of the higher molecular compounds, it is possible to start directly from a water containing crude oxidation products, evaporating expenses thus being saved when working with such starting materials.

Aliphatic hydrocarbons, such as' gasoline, petrol, ligroin, etc., have proved to be particularly suitable as non-polar solvent liquids. The number of these liquids is comparatively large, so that a complete list thereof cannot be given. However, those skilled in the art can easily determine'which amount the large group of non solvent liquids is most suitable for any particular proceed- 1ng.

The following examples are given to further illustrate the method of the present invention, the scope of the invention not however being limited to the specific details of the examples.

Example I parts of a dry mixture of carboxylic acids obtained by oxidizing treatment of hard coal with nitric acid at superatmospheric pressure and in the presence of oxygen gas, and by subsequentlydistilling off the unconsumed nitric acid, are heated inan iron vessel at 220 C., for 5 hours. Simultaneously, superheated steam at 220 C. is passed through the acid mixture distributed upon a layer of pumice in order to carry away the volatile constituents. The waste gases contain carbon dioxide and perceptible amounts of picric acid formed as by-product during the oxidizing treatment of the coal.

After the aforesaid treatment, the dry residue which is free of picric acid is digested with 7.5 times its volume of water. The insoluble substance (27 parts) is removed and the aqueous liquid evaporated. 53 parts of a mixture of carboxylic acids are obtained, said mixture consisting substantially of benzene di t'ri-, tetra-, and pentacarboxylic acid, in addition to adipinic acid and succinic acid. The separated insoluble-part consistsof multinuclear aromatic acids the nature of which'are' i partially This part was rendered insolu- 100 parts of a crude mixture of carboxylic acids obtrained by an oxidizing treatment of hard coal with nitric acid under super-atmospheric pressure are dissolved in 500, parts of water and heated for hours at 200 CI and under 15 atmospheres pressure in a stirring autoclave. The carbon dioxide evolved hereby is allowed to cdntinuously blow' off. The precipitated substance (dry weight 38.0 parts) is removed and the remaining liquid diluted with water to double its volume. The thus precipitated substance is filtered off. Upon evaporating the solution, 47.0 parts of a light-yellow mixture of carboxylic acids,of.the composition specified in Example I, are obtained. These can be purified again by recrystallizing from dilute nitric acid.

Example III Example IV 100 parts of a dark brown crude mixture of carboxylic' acids obtained by oxidation of coal with nitric acid are dissolved in 500 parts of methanol and heated during 8' hours to 200" C. in an autoclave. After cooling, the precipitated substance is filtered ofl? and washed with methanol, the dry weight of said substance being 47 parts. The methanolic solution is evaporated in order to remove the methanol and the mixture of esters treated with chlorine until colorless. The decolorized product is diluted with ten times its volume of water and the mixture subjected to hydrolysis at 180 C. and under 10. atmospheres pressure. The aqueous solution obtained is of light-yellow color, containing partially chlorinated carboxylic acids, mainly mellithic acid, benzene pentaearboxylic acid, pyromellithic acid, mellophanic acid, trimellithic acid, phthalic acid and succinic acid.

Example V 100 parts of a dark-brown crude mixture of carboxylic acids, obtained by an oxidizing treatment of coal with nitric acid are dissolved in 500 parts of methanol and heated in an autoclave during 8 hours to 200 C. After cooling, the precipitated substance is filtered oil and washed with methanol, the dry weight of said substance being 47 parts. The methanolic solution is separated and the remainder distilled in vacuo at 0.1 mm. Hg pressure. The distillate is heated for 10 minutes with 10 parts of concentrated nitric acid, then diluted with water to ten times its volume and hydrolyzed at 180 C. and at 10 atmospheres pressure. The aqueous solution resulting is of light-yellow color, containing substantially mellithic acid, benzene pentacarboxylicacid, pyromellithic acid, mellophanic acid, trimellithic acid, phthalic acid and succinic acid.

Example VI 100 parts of a. crude mixture of carboxylic acid obtained according to Example I are dissolved in 500 parts of propanol and heated in an autoclave during 5 hours to 200 C. After cooling, the precipitated substance is filtered off and the filtrate dried with dehydrated sodium sulfate. The substance additionally precipitated hereby is removed together with the'sodium sulfate and the solution heated again to: 200 C... for 3 hours. The; mixture of esters formed is decolorized by introducing" chlorine, a slight chlorination being involved thereby,"

and subsequentlydistilled in vacuo'at 0.1 mm. .Hg of pressure. 40 parts of a slightly chlorinated mixture of propyl esters are obtained which can be utilized as plasticizer for various purposes.

Example VII parts of a crude mixture of carboxylic acids obtained by an oxidizing treatment of coal at 160 C. withnitric acid are dissolved in 300 parts of water, 2 parts of zinc nitrate (Zn(NO -6I-I O) being added to the solu-.- tion. During one hour the solution is heated to 230 C. in an autoclave. After cooling, the solution is filtered and the light-colored filtrate neutralized by adding so.- dium hydroxide solution (30%) whereupon the same quantityof NaOH is added once more. Subsequently, 5 parts of potassium permanganate are added and the solution is kept boiling during one hour. After cooling, the filtrate is acidulated with hydrochloric acid and extracted with butanone. Upon evaporating the butanone, almost colorless crystals of carboxylic acids are obtained, the quantity of which vary according to the conditions under which the coal is oxidized; generally this quantity amounts to about 30-35% of the weight of the crude mixture of carboxylic acids employed.

Example VIII parts of an oxidation product obtained by oxidiz' ing treatment of a gas flame coal with nitric acid (density 1.2), at superatmospheric pressure, said product being free of unreacted nitric acid, yet containing still 50 parts of water, are mixed with 130 parts of butanol and 400 parts of petrol spirit (boiling range 100-l20 C.) and, subsequently slowly heated to 190 C. in a stirring autm clave for several hours; The pressure is kept between- 5 and 6 atmospheres by a control valve, if need be, by adding a gas (nitrogen or hydrogen). The water distilled off together with butanol and petrol spirit is separated in a trap, the organic dissolving agents being refluxed to the reactor by means of a syphon. After cooling and releasing the pressure, 73 parts of the grainy substance are filtered oil. The organic dissolving agents are removed from the filtrate by distillation, 77 parts of a crude ester mixture remaining (acid number 8). After distillation under vacuum in a still operated according to the .falling-film principle, 50.2 parts of a pure butylic ester are obtained, in addition to 26 parts of a brilliant black pitch-like product solidifying in the cold.

Example IX 100 parts of a dry oxidation product obtained accord ing to Example VIII are digested in 180 parts of butanol and 250 parts of ligroin and subsequently esterified at C. under 5 atmospheres pressure in a stirring autoclave. After cooling and releasing the pressure, 69 parts of the precipitated substance are removed. The organic dissolving liquids are distilled oii, leaving a crude mixture of esters which is Worked up according to Example VIII. 48 parts of an ester distillate are obtained, in addition to 23 parts of a viscous bituminous product.

Without further analysis, the foregoing will so fully reveal the gist of the present invention that others can by applying current knowledge readily adapt it for var ious applications without omitting features that, from the standpoint of prior art, fairly constitute essential characteristics of the generic or specific aspects of this: invention and, therefore, such adaptations should and are intended to be comprehended within the meaning and range of equivalence of the following claims.

What is claimed as new and desired to be secured by Letters Patent is:

l. A method of obtaining a light-colored mixture of. benzene carboxylic acids and aliphatic carboxylic acids from a product obtained by the oxidation of a carbo naceous material selected from-the group consisting of bituminous coal, lignites, peat, coke, tar and pitch with nitric acid and containing said light-colored benzene and aliphatic carboxylic acids which are soluble in water and also containing dark-colored polycyclic acids which are soluble in water in the presence of said benzene and aliphatic carboxylic acids, comprising the steps of heating said product at a temperature above 100 C. and up to 250 C. for a time sufiicient to decarboxylate said dark-colored polycyclic acids and convert the same to a chemically difierent product insoluble in water even in the presence of said benzene and aliphatic carboxylic acids; and separating said water-soluble light-colored benzene and aliphatic carboxylic acids from said chemically difierent product which is water-insoluble.

2. A method of obtaining a light-colored mixture of benzene carboxylic acids and aliphatic carboxylic acids from a dry product obtained by the oxidation of a carbonaceous material selected from the group consisting of bituminous coal, lignites, peat, coke, tar and pitch with nitric acid and containing said light-colored benzene and aliphatic carboxylic acids which are soluble in water and also containing dark-colored polycyclic acids which are soluble in water in the presence of said benzene and aliphatic carboxylic acids, comprising the steps of heating said dry product in the absence of water at a temperature above 100 C. and up to 250 C. for a time sufiicient to decarboxylate said dark-colored polycyclic acids and convert the same to a chemically different product insoluble in water even in the presence of said benzene and aliphatic carboxylic acids; and separating said water soluble light-colored benzene and aliphatic carboxylic acids from said chemically different product which is water-insoluble.

3. A method of obtaining a light-colored mixture of benzene carboxylic acids and aliphatic carboxylic acids from a product obtained by the oxidation of a carbonaceous material selected from the group consisting of bituminous coal, lignites, peat, coke, tar and pitch with nitric acid and containing said light-colored benzene and aliphatic carboxylic acids which are soluble in water and also containing dark-colored polycyclic acids which are soluble in water in the presence of said benzene and aliphatic carboxylic acids, comprising the steps of heating said product in the presence of an organic solvent in which said benzene and aliphatic carboxylic acids are soluble at a temperature above 100 C. and up to 250 C. for a time sufficient to decarboxylate said dark-colored polycyclic acids and convert the same to a chemically different product insoluble in water even in the presence of said benzene and aliphatic carboxylic acids, thereby forming a reaction mass consisting essentially of said benzene and aliphatic carboxylic acids dissolved in said organic solvent therefor and said chemically different product which remains undissolved; and separating said solution of said water-soluble light-colored benzene and aliphatic carboxylic acids from said chemically difierent product.

4. A method of obtaining a light-colored mixture of benzene carboxylic acids and aliphatic carboxylic acids from a product obtained by the oxidation of a carbonaceous material selected from the group consisting of bituminous coal, lignites, peat, coke, tar and pitch with nitric acid and containing said light-colored benzene and aliphatic carboxylic acids which are soluble in water and also containing dark-colored polycyclic acids which are soluble in water in the presence of said benzene and aliphatic carboxylic acids, comprising the steps of heating said product in the presence of water at a temperature above 100 C. and up to 250 C. for a time suificient to decarboxylate said dark-colored polycyclic acids and convert the same to a chemically difierent product insoluble in water even in the persence of said benzene and aliphatic carboxylic acids, thereby forming a reaction mass consisting essentially of an aqueous solution of 5. A method of obtaining a light-colored mixture, of

benzene carboxylic acids and aliphatic carboxylic acids from a product obtained by the oxidation of a carbonaceous material selected from the group consisting of bituminous coal, lignites, peat, coke, tar and pitch with nitric acid and containing said light-colored benzene and aliphatic carboxylic acids which are soluble in water and also containing dark-colored polycyclic acids which are soluble in water in the presence of said benzene and aliphatic carboxylic acids, comprising the steps of heating said product at least partly dissolved in an alcohol at a temperature above C. and up to 250 C. for a time suflicient to decarboxylate said dark-colored polycyclic acids and convert the same to a chemically different product insoluble in water even in the presence of said benzene and aliphatic carboxylic acids while at the same time esterifying said benzene and aliphatic carboxylic acids with said alcohol, thereby forming a reaction mass consisting essentially of said chemically different product which remains undissolved and dissolved esters of said benzene and aliphatic carboxylic acids; and separating said dissolved esters of said light-colored benzene and aliphatic carboxylic acids from said chemically different product.

6. A method of obtaining a light'colored mixture of benzene carboxylic acids and aliphatic carboxylic acids from a product obtained by the oxidation of a carbonaceous material selected from the group consisting of bituminous coal, lignites, peat, coke, tar and pitch with nitric acid and containing said light-colored benzene and aliphatic carboxylic acids which are soluble in water and also containing dark-colored polycyclic acids which are soluble in water in the presence of said benzene and aliphatic carboxylic acids, comprising the steps of heating said product in the presence of at least one salt of a metal selected from the group consisting of the first, second and eighth groups of the periodic system at a temperature above 100 C. and up to 250 C. for a time sufficient to decarboxylate said darkcolored polycyclic acids and convert the same to a chemically difit'erent product insoluble in water even in the presence of said benzene and aliphatic carboxylic acids; and separating said water-soluble light-colored ben zene and aliphatic carboxylic acids from said chemically dilferent product which is water-insoluble.

7. A method of obtaining a light-colored mixture of benzene carboxylic acids and aliphatic carboxylic acids from a product obtained by the oxidation of a carbona ceous material selected from the group consisting of bituminous coal, lignites, peat, coke, tar and pitch with nitric acid and containing said light-colored benzene and aliphatic carboxylic acids which are soluble in water and also containing dark-colored polycyclic acids which are soluble in water in the presence of said benzene and aliphatic carboxylic acids, comprising the steps of heating said product at least partly dissolved in an organic liquid comprising an alcohol and a non-polar organic solvent for said benzene and aliphatic carboxylic acids at a temperature about 100 C. and up to 250 C. for several hours so as to decarboxylate said dark-colored polycyclic acids and convert the same to a chemically different product insoluble in water even in the presence of said benzene and aliphatic carboxylic acids while at the same time esterifying said benzene and aliphatic carboxylic acids with said alcohol, thereby forming a reaction mass consisting essentially of said chemically different product which remains undissolved and dissolved esters of said benzene and aliphatic carboxylic acids; and separating said dissolved esters of said light,

colored benzene and fliphatie c at boxyliq acidsfrom 2,623,216 said chemically difiercnt product. 2,726,262

- I 2,785,198 Refgrence; Cited; in the file= of this patent UNITED STATES PATENTS 635 008 7 2,640,075 Goedkoop Ma 26, 1953 I2 Gocdkmop Mar. 23, 1954" Gros'skinsky et a1 Dec. 6;1955 Grosskinsky et a1. Mar. 12, 1957 FOREIGN PATENTS Great Britain Apr. 5, 1950 

5. A METHOD OF OBTAINING A LIGHT-COLORED MIXTURE OF BENZENE CARBOXYLIC ACIDS AND ALIPHATIC CARBOXYLIC ACIDS FROM A PRODUCT OBTAINED BY THE OXIDATION OF A CARBONACEOUS MATERIAL SELECTED FROM THE GROUP CONSISTING OF BITUMINOUS COAL, LIGNITES, PEAT, COKE, TAR AND PITCH WITH NITRIC ACID AND CONTAINING SAID LIGHT-COLORED BENZENE AND ALIPHATIC CARBOXYLIC ACIDS WHICH ARE SOLUBLE IN WATER AND ALSO CONTAINING DARK-COLORED POLYCYLIC ACIDS WHICH ARE SOLUBLE IN WATER IN THE PRESENCE OF SAID BENZENE AND ALIPHATIC CARBOXYLIC ACIDS, COMPRISING THE STEPS OF HEATING SAID PRODUCT AT LEAST PARTLY DISSOLVED IN AN ALCOHOL AT A TEMPERATURE ABOVE 100* C. AND UP TO 250* C. FOR A TIME SUFFICIENT TO DECARBOXYLATE SAID DARK-COLORED POLYCYCLIC ACIDS AND CONVERT THE SAME TO A CHEMICALLY DIFFERENT PRODUCT INSOLUBLE IN WATER EVEN IN THE PRESENCE OF SAID BENZENE AND ALIPHATIC CARBOXYLIC ACIDS WHILE AT THE SAME TIME ESTERIFYING SAID BENZNE AND ALIPHATIC CARBOXYLIC ACIDS WITH SAID ALCOHOL, THEREBY FORMING A REACTION MASS CONSISTING ESSENTIALLY OF SAID CHEMICALLY DIFFERENT PRODUCT WHICH REMAINS UNDISSOLVED AND DISSOLVED ESTERS OF SAID BENZENE AND ALIPHATIC CARBOXYLIC ACIDS; AND SEPARATING SAID DISSOLVED ESTERS OF SAID LIGHT-COLORED BENZENE AND ALIPHATIC CARBOXYLIC ACIDS FROM SAID CHEMICALLY DIFFERENT PRODUCT. 